React Activation

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HACK Implementation of the <keep-alive /> function in Vue For React

Please also pay attention to official support <Offsreen /> in React 18.x

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More stable <KeepAlive /> function with babel pre-compilation

Online Demo

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More examples

• Closable tabs with react-router
• Closable tabs with umi
• Using Animation with react-router

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Compatibility

• React v17+ (beta)

• React v16+

• Preact v10+

• Compatible with SSR

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Install

yarn add react-activation
# or
npm install react-activation

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Usage

1. Add react-activation/babel plugins in .babelrc

Why is it needed?

The plugin adds a _nk attribute to each JSX element during compilation to help the react-activation runtime generate an unique identifier by render location base on react-node-key.

{
  "plugins": [
    "react-activation/babel"
  ]
}

2. Wrap the components that need to keep states with <KeepAlive>

Like the <Counter> component in the example

// App.js

import React, { useState } from 'react'
import KeepAlive from 'react-activation'

function Counter() {
  const [count, setCount] = useState(0)

  return (
    <div>
      <p>count: {count}</p>
      <button onClick={() => setCount(count => count + 1)}>Add</button>
    </div>
  )
}

function App() {
  const [show, setShow] = useState(true)

  return (
    <div>
      <button onClick={() => setShow(show => !show)}>Toggle</button>
      {show && (
        <KeepAlive>
          <Counter />
        </KeepAlive>
      )}
    </div>
  )
}

export default App

3: In your business code, place the <AliveScope> outer layer at a location that will not be unmounted, usually at the application entrance

While using React 16.x, with [email protected], there is no longer necessary to place the outer layer of <AliveScope>

In React 17.x, due to the change of the event monitoring method, the outer layer of <AliveScope> still needs to be placed

Note: When used with react-router or react-redux, you need to place <AliveScope> inside <Router> or <Provider>

// index.js

import React from 'react'
import ReactDOM from 'react-dom'
import { AliveScope } from 'react-activation'

import App from './App'

ReactDOM.render(
  <AliveScope>
    <App />
  </AliveScope>,
  document.getElementById('root')
)

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Lifecycle

ClassComponent works with withActivation decorator

Use componentDidActivate and componentWillUnactivate to correspond to the two states of "activate" and "unactivate" respectively.

FunctionComponent uses the useActivate and useUnactivate hooks respectively

...
import KeepAlive, { useActivate, useUnactivate, withActivation } from 'react-activation'

@withActivation
class TestClass extends Component {
  ...
  componentDidActivate() {
    console.log('TestClass: componentDidActivate')
  }

  componentWillUnactivate() {
    console.log('TestClass: componentWillUnactivate')
  }
  ...
}
...
function TestFunction() {
  useActivate(() => {
    console.log('TestFunction: didActivate')
  })

  useUnactivate(() => {
    console.log('TestFunction: willUnactivate')
  })
  ...
}
...
function App() {
  ...
  return (
    {show && (
      <KeepAlive>
        <TestClass />
        <TestFunction />
      </KeepAlive>
    )}
  )
}
...

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Save Scroll Position (true by default)

<KeepAlive /> would try to detect scrollable nodes in its children, then, save their scroll position automaticlly before componentWillUnactivate and restore saving position after componentDidActivate

If you don't want <KeepAlive /> to do this thing, set saveScrollPosition prop to false

<KeepAlive saveScrollPosition={false} />

If your components share screen scroll container, document.body or document.documentElement, set saveScrollPosition prop to "screen" can save sharing screen container's scroll position before componentWillUnactivate

<KeepAlive saveScrollPosition="screen" />

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Multiple Cache

Under the same parent node, <KeepAlive> in the same location will use the same cache by default.

For example, with the following parameter routing scenario, the /item route will be rendered differently by id, but only the same cache can be kept.

<Route
  path="/item/:id"
  render={props => (
    <KeepAlive>
      <Item {...props} />
    </KeepAlive>
  )}
/>

Similar scenarios, you can use the id attribute of <KeepAlive> to implement multiple caches according to specific conditions.

<Route
  path="/item/:id"
  render={props => (
    <KeepAlive id={props.match.params.id}>
      <Item {...props} />
    </KeepAlive>
  )}
/>

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Cache Control

Automatic control cache

Add the when attribute to the <KeepAlive /> tag that needs to control the cache. The value is as follows

When the when type is Boolean

• true: Cache after uninstallation
• false: Not cached after uninstallation

<KeepAlive when={false}>

When the when type is Array

The 1th parameter indicates whether it needs to be cached at the time of uninstallation.

The 2th parameter indicates whether to unload all cache contents of <KeepAlive>, including all <KeepAlive> nested in <KeepAlive>.

// For example:
// The following indicates that it is not cached when uninstalling
// And uninstalls all nested `<KeepAlive>`
<KeepAlive when={[false, true]}>
  ...
  <KeepAlive>
    ...
    <KeepAlive>...</KeepAlive>
    ...
  </KeepAlive>
  ...
</KeepAlive>

When the when type is Function

The return value is the above Boolean or Array, which takes effect as described above.

Manually control the cache

1. Add the name attribute to the <KeepAlive> tag that needs to control the cache.

2. Get control functions using withAliveScope or useAliveController

   • drop(name)

     Unload the <KeepAlive> node in cache state by name. The name can be of type String or RegExp. Note that only the first layer of content that hits <KeepAlive> is unloaded and will not be uninstalled in <KeepAlive>. Would not unload nested <KeepAlive>

   • dropScope(name)

     Unloads the <KeepAlive> node in cache state by name. The name optional type is String or RegExp, which will unload all content of <KeepAlive>, including all <KeepAlive> nested in <KeepAlive>.

   • clear()

     will clear all <KeepAlive> in the cache

   • getCachingNodes()

     Get all the nodes in the cache

...
import KeepAlive, { withAliveScope, useAliveController } from 'react-activation'
...
<KeepAlive name="Test">
  ...
    <KeepAlive>
      ...
        <KeepAlive>
          ...
        </KeepAlive>
      ...
    </KeepAlive>
  ...
</KeepAlive>
...
function App() {
  const { drop, dropScope, clear, getCachingNodes } = useAliveController()

  useEffect(() => {
    drop('Test')
    // or
    drop(/Test/)
    // or
    dropScope('Test')

    clear()
  })

  return (
    ...
  )
}
// or
@withAliveScope
class App extends Component {
  render() {
    const { drop, dropScope, clear, getCachingNodes } = this.props

    return (
      ...
    )
  }
}
...

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Principle

Pass the children attribute of <KeepAlive /> to <AliveScope /> and render it with <Keeper />

After rendering <Keeper />, the content is transferred to <KeepAlive /> through DOM operation.

Since <Keeper /> will not be uninstalled, caching can be implemented.

Simplest Implementation Demo

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Breaking Change

1. <KeepAlive /> needs to pass children to <AliveScope /> , so the rendering of the real content will be slower than the normal situation

   Will have a certain impact on the function of strictly relying on the lifecycle order, such as getting the value of ref in componentDidMount, as follows

   class Test extends Component {
     componentDidMount() {
       console.log(this.outside) // will log <div /> instance
       console.log(this.inside) // will log undefined
     }
   
     render() {
       return (
         <div>
           <div
             ref={ref => {
               this.outside = ref
             }}
           >
             Outside KeepAlive
           </div>
           <KeepAlive>
             <div
               ref={ref => {
                 this.inside = ref
               }}
             >
               Inside KeepAlive
             </div>
           </KeepAlive>
         </div>
       )
     }
   }

   The above error in ClassComponent can be fixed by using the withActivation high-level component

   FunctionComponent currently has no processing method, you can use setTimeout or nextTick to delay ref getting behavior

   @withActivation
   class Test extends Component {
     componentDidMount() {
       console.log(this.outside) // will log <div /> instance
       console.log(this.inside) // will log <div /> instance
     }
   
     render() {
       return (
         <div>
           <div
             ref={ref => {
               this.outside = ref
             }}
           >
             Outside KeepAlive
           </div>
           <KeepAlive>
             <div
               ref={ref => {
                 this.inside = ref
               }}
             >
               Inside KeepAlive
             </div>
           </KeepAlive>
         </div>
       )
     }
   }

2. Destructive impact on Context

   after [email protected] with [email protected]+, this question has been automatic fixed

   [email protected] with react@17+ you Need to make the following changes to achieve automatic repair

   import { autoFixContext } from 'react-activation'
   
   autoFixContext(
    [require('react/jsx-runtime'), 'jsx', 'jsxs', 'jsxDEV'],
    [require('react/jsx-dev-runtime'), 'jsx', 'jsxs', 'jsxDEV']
   )

   Versions below [email protected] need to be repaired manually, refer to the following

   Problem reference: StructureBuilder/react-keep-alive#36

   <Provider value={1}>
     {show && (
       <KeepAlive>
         <Consumer>
           {(
             context // Since the rendering level is broken, the context cannot be obtained here.
           ) => <Test contextValue={context} />}
         </Consumer>
       </KeepAlive>
     )}
     <button onClick={toggle}>toggle</button>
   </Provider>

   Choose a repair method

   • Create Context using createContext exported from react-activation

   • Fix the affected Context with fixContext exported from react-activation

   ...
   import { createContext } from 'react-activation'
   
   const { Provider, Consumer } = createContext()
   ...
   // or
   ...
   import { createContext } from 'react'
   import { fixContext } from 'react-activation'
   
   const Context = createContext()
   const { Provider, Consumer } = Context
   
   fixContext(Context)
   ...

3. Affects the functionality that depends on the level of the React component, as follows

   • Fix withRouter/hooks of react-router
   • Error Boundaries (Fixed)
   • React.Suspense & React.lazy (Fixed)
   • React Synthetic Event Bubbling Failure
   • Other undiscovered features

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